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Implement parallel version of mergesort

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This commit is contained in:
Robin Dietzel 2023-11-01 11:57:18 +01:00
parent 304af488ce
commit c560bfe4cc
2 changed files with 145 additions and 8 deletions
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43
task1/main.cpp
View File

@ -44,23 +44,54 @@ auto main(int argc, char *argv[]) -> int {
return -1;
}
fmt::print("Opened file {} sucessfully!\n", "dummy");
fmt::print("Opened file {} sucessfully\n", "dummy");
std::vector<int32_t> dataset;
parse_file(file, dataset);
fmt::print("Read {} values from {}\n", dataset.size(), "dummy");
auto t1 = std::chrono::high_resolution_clock::now();
auto dataset_par = dataset;
auto dataset_seq = dataset;
algo::MergeSort_v1::sort(dataset.begin(), dataset.end(), [](int32_t a, int32_t b) {
auto t1 = std::chrono::high_resolution_clock::now();
algo::MergeSort_v1::sort(dataset_seq.begin(), dataset_seq.end(), [](int32_t a, int32_t b) {
return (a > b);
});
auto t2 = std::chrono::high_resolution_clock::now();
auto delay_ms = std::chrono::duration_cast<std::chrono::milliseconds>(t2 - t1);
fmt::print("Sorted {} entries within {} ms.", dataset.size(), delay_ms.count());
fmt::print("Sorted {} entries within {} ms in sequential\n", dataset_seq.size(), delay_ms.count());
t1 = std::chrono::high_resolution_clock::now();
algo::MergeSort_v2::sort(dataset_par.begin(), dataset_par.end(), [](int32_t a, int32_t b) {
return (a > b);
}, 16);
t2 = std::chrono::high_resolution_clock::now();
delay_ms = std::chrono::duration_cast<std::chrono::milliseconds>(t2 - t1);
fmt::print("Sorted {} entries within {} ms in parallel using {} threads\n", dataset_seq.size(), delay_ms.count(), 16);
auto eq = (dataset_seq == dataset_par);
fmt::print("Equality: {}\n", eq);
fmt::print("Parallel dataset: {}; Sequential dataset: {}\n", dataset_par.size(), dataset_seq.size());
//fmt::print("Created {} recurstions", algo::MergeSort_v1::get_recursions());
std::ofstream ofile("dataset.out.dat", std::ios_base::out);
if(!ofile.is_open()) {
fmt::print("Error writing to file");
return -1;
}
for(auto &element : dataset_seq) {
ofile << std::to_string(element) << '\n';
}
file.close();
ofile.flush();
ofile.close();
fmt::print("Written to output file\n");
return 0;

110
task1/mergesort.h
View File

@ -2,13 +2,16 @@
#include <vector>
#include <algorithm>
#include <thread>
#include <mutex>
namespace algo {
class MergeSort_v1 {
private:
template<typename Iterator, typename Comparator>
static auto merge(Iterator start, Iterator middle, Iterator end, Comparator cmp, Iterator output_start) -> void {
static auto
merge(Iterator start, Iterator middle, Iterator end, Comparator cmp, Iterator output_start) -> void {
Iterator start_m = start;
Iterator begin = output_start;
Iterator start2 = middle + 1;
@ -46,7 +49,8 @@ namespace algo {
}
template<typename Container, typename Iterator, typename Comparator>
static auto ms_split(Container &output_vec, Iterator start, Iterator end, Comparator cmp, Iterator output_start) -> void {
static auto
ms_split(Container &output_vec, Iterator start, Iterator end, Comparator cmp, Iterator output_start) -> void {
Iterator mid = start;
Iterator begin = output_start;
@ -77,4 +81,106 @@ namespace algo {
}
};
class MergeSort_v2 {
private:
//Caution: non thread-safe, must be executed with additional protection (e.g. lock_guard)
template<typename Iterator, typename Comparator>
static auto
merge(Iterator start, Iterator middle, Iterator end, Comparator cmp, Iterator output_start) -> void {
Iterator start_m = start;
Iterator begin = output_start;
Iterator start2 = middle + 1;
//merge from input until one half completes
while (start <= middle && start2 <= end) {
if (cmp(*start, *start2)) {
*output_start = *start;
start++;
} else {
*output_start = *start2;
start2++;
}
output_start++;
}
//try to finish first half
while (start <= middle) {
*output_start = *start;
start++;
output_start++;
}
while (start2 <= end) {
*output_start = *start2;
start2++;
output_start++;
}
const auto size = std::distance(start_m, end);
for (auto i = 0; i <= size; i++, start_m++, begin++) {
*start_m = *begin;
}
}
template<typename Container, typename Iterator, typename Comparator>
static auto ms_split(Container &output_vec, Iterator start, Iterator end, Comparator cmp, Iterator output_start,
int &nthreads, std::mutex &dataset_guard, std::mutex &depth_guard) -> void {
Iterator mid = start;
Iterator begin = output_start;
if (std::distance(start, end) < 1) {
return;
} else {
if (nthreads > 1) {
depth_guard.lock();
nthreads -= 2;
depth_guard.unlock();
//move mid iterator litterally to the mid
std::advance(mid, std::distance(start, end) / 2);
//sort the first half within an recursion
std::thread t1([&]() { ms_split(output_vec, start, mid, cmp, output_start, nthreads, dataset_guard, depth_guard); });
//move output iteratoroutput_vec, start, mid, cmp, output_start
std::advance(output_start, std::distance(start, mid + 1));
//sort the second half within a recursion
std::thread t2([&]() { ms_split(output_vec, mid + 1, end, cmp, output_start, nthreads, dataset_guard, depth_guard); });
//merge everything together starting from the complete beginning
t1.join();
t2.join();
const std::lock_guard<std::mutex> lock(dataset_guard);
merge(start, mid, end, cmp, begin);
} else {
//move mid iterator litterally to the mid
std::advance(mid, std::distance(start, end) / 2);
//sort the first half within an recursion
ms_split(output_vec, start, mid, cmp, output_start, nthreads, dataset_guard, depth_guard);
//move output iterator
std::advance(output_start, std::distance(start, mid + 1));
//sort the second half within a recursion
ms_split(output_vec, mid + 1, end, cmp, output_start, nthreads, dataset_guard, depth_guard);
//merge everything together starting from the complete beginning
const std::lock_guard<std::mutex> lock(dataset_guard);
merge(start, mid, end, cmp, begin);
}
}
}
public:
template<typename Iterator, typename Comparator>
static auto sort(Iterator start, Iterator end, Comparator cmp, int nthreads) -> void {
using valtype = typename std::iterator_traits<Iterator>::value_type;
std::vector<valtype> temporary_dataset(std::distance(start, end));
std::mutex dataset_guard;
std::mutex depth_guard;
ms_split(temporary_dataset, start, end - 1, cmp, temporary_dataset.begin(), nthreads, dataset_guard, depth_guard);
}
};
}